One major aim of this project is to characterize the chemical and biological properties of the growth hormone circulating in the blood. For this work, the blood of rats bearing the mammotropic-somatotropic tumor MtTW15 will be used. An attempt will be made to utilize affinity chromatography to isolate the circulating hormone, so that it may be characterized chemically and biologically. A related aim is to determine whether acute fluctuations in the level of circulating growth hormone are reflected in alterations in metabolic activity of the organism. As part of the long-term goal of this project, which is to inquire into the mechanism of the anabolic action of growth hormone, efforts will be made to study the initial metabolic events that occur in muscle after interaction of growth hormone with its receptors. In this work, antibodies against rat growth hormone will be used to remove or neutralize growth hormone bound to its receptors on the isolated rat diaphragm. BIBLIOGRAPHIC REFERENCES: Isaksson, O., Gimpel, L. P., Ahren, K. and Kostyo, J. L. Growth hormone and cyclic AMP in rat diaphragm muscle. Acta endocrinol. 77 (Suppl. 191): 73-80, 1974. Kostyo, J. L., Gimpel, L. P. and Isaksson, O. In vitro effects of growth hormone on cyclic AMP metabolism in the isolated rat diaphragm. Adv. Metab. Dis. 8: 249-262, 1975.